I feel like they were roughly equal, so it would go either way. It could be that since Roger was stronger than Garp, Rayleigh was stronger than Sengoku(or Rayleigh being on par with Garp). Kinda like how Luffy is stronger than Smoker and Zoro is stronger than Tashigi(Smoker and Zoro could be on par at the moment). And Shiki, for me, was the weakest one amongst these legends from the old sea.
Roger=Whitebeard>Garp>=Rayleigh=Sengoku>Shiki.